In haloalkanes, the halogen atom is attached to carbon atom. As the halogen atom is more electronegative than carbon, the bond between carbon and halogen is polar in character.
Due to presence of partial positive charge on carbon atom, the nucleophiles can attack on electron deficient carbon thereby resulting in the displacement of weaker nucleophile, thus typical reactions of alkyl halides are nucleophilic substitution reactions :
Whereas in haloarenes, as the halogen atom attached to benzene ring, releases electron towards benzene ring (+m effect) thereby the ortho and para positions become site of attack for electrophiles more than nucleophiles.
